gfs2: Fix possible data races in gfs2_show_options()

Some fields such as gt_logd_secs of the struct gfs2_tune are accessed
without holding the lock gt_spin in gfs2_show_options():

  val = sdp->sd_tune.gt_logd_secs;
  if (val != 30)
    seq_printf(s, ",commit=%d", val);

And thus can cause data races when gfs2_show_options() and other functions
such as gfs2_reconfigure() are concurrently executed:

  spin_lock(&gt->gt_spin);
  gt->gt_logd_secs = newargs->ar_commit;

To fix these possible data races, the lock sdp->sd_tune.gt_spin is
acquired before accessing the fields of gfs2_tune and released after these
accesses.

Further changes by Andreas:

- Don't hold the spin lock over the seq_printf operations.

Reported-by: BassCheck <bass@buaa.edu.cn>
Signed-off-by: Tuo Li <islituo@gmail.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 3a7e7c3..c89b280 100644 (file)
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -1004,7 +1004,14 @@ static int gfs2_show_options(struct seq_file *s, struct dentry *root)
 {
        struct gfs2_sbd *sdp = root->d_sb->s_fs_info;
        struct gfs2_args *args = &sdp->sd_args;
-       int val;
+       unsigned int logd_secs, statfs_slow, statfs_quantum, quota_quantum;
+
+       spin_lock(&sdp->sd_tune.gt_spin);
+       logd_secs = sdp->sd_tune.gt_logd_secs;
+       quota_quantum = sdp->sd_tune.gt_quota_quantum;
+       statfs_quantum = sdp->sd_tune.gt_statfs_quantum;
+       statfs_slow = sdp->sd_tune.gt_statfs_slow;
+       spin_unlock(&sdp->sd_tune.gt_spin);
 
        if (is_ancestor(root, sdp->sd_master_dir))
                seq_puts(s, ",meta");
@@ -1059,17 +1066,14 @@ static int gfs2_show_options(struct seq_file *s, struct dentry *root)
        }
        if (args->ar_discard)
                seq_puts(s, ",discard");
-       val = sdp->sd_tune.gt_logd_secs;
-       if (val != 30)
-               seq_printf(s, ",commit=%d", val);
-       val = sdp->sd_tune.gt_statfs_quantum;
-       if (val != 30)
-               seq_printf(s, ",statfs_quantum=%d", val);
-       else if (sdp->sd_tune.gt_statfs_slow)
+       if (logd_secs != 30)
+               seq_printf(s, ",commit=%d", logd_secs);
+       if (statfs_quantum != 30)
+               seq_printf(s, ",statfs_quantum=%d", statfs_quantum);
+       else if (statfs_slow)
                seq_puts(s, ",statfs_quantum=0");
-       val = sdp->sd_tune.gt_quota_quantum;
-       if (val != 60)
-               seq_printf(s, ",quota_quantum=%d", val);
+       if (quota_quantum != 60)
+               seq_printf(s, ",quota_quantum=%d", quota_quantum);
        if (args->ar_statfs_percent)
                seq_printf(s, ",statfs_percent=%d", args->ar_statfs_percent);
        if (args->ar_errors != GFS2_ERRORS_DEFAULT) {